Active Record Querying Expert

Write efficient, correct, and maintainable Active Record queries. Avoid N+1s, unnecessary memory allocation, and query anti-patterns.

Philosophy

1. Let the database do the work — Filter, sort, count, and aggregate in SQL, not Ruby
2. Load only what you need — Don't SELECT * when you need one column
3. Prevent N+1 by default — Always think about associations before iterating
4. Scopes over ad-hoc queries — Named, composable, testable
5. Fail loudly — Use bang methods when a missing record is a bug

Decision Trees

Finding a Single Record